This invention relates to a communication system and, more particularly, to a communication system having remotely controllable signal receiving means.
In a communication system such as an electronic switching system, a terminal device is generally accommodated in the system via a corresponding line circuit. When the terminal device originates a call, a start signal is inputted at the line circuit via a pair of communication lines. Such start signals are classified into two types: "a loop-start signal" which is transmitted to the line circuit through a closed loop formed in the communication lines and "a ground-start signal" which is transmitted to the line circuit through one of the pair of communication lines. The start signals are selectively used depending on the type of the terminal device. When the terminal device in an electronic switching system is a coin telephone set or a private branch exchange, the ground-start signal is used. When the terminal device is a regular telephone set, on the other hand, the loop-start signal is used. Such a line circuit is preferably constructed for general purpose to receive both types of start signals and detect a call originating from the terminal device.
In the prior art, a plurality of line circuits constructed for general purpose are packaged on a printed circuit board to meet the above requirement. The packaged line circuits are generally called a line circuit card or a line card. The line circuit card is provided with a signal receiving function by jumper wire connection on the board or by a manual switching operation on the board. The line circuit card is then inserted (mounted) at a predetermined location in communication equipment to satisfy a predetermined station design condition, that is, a type of a start signal used by a terminal device in an initial period of construction at a system installation place (a communication station).
However, since the function of receiving the start signal is manually provided to each of several thousand of the line circuits at the station by maintenance workers, the period required for the initial construction is long, and function setting errors inevitably occur, simultaneously. The opportunity for error increases when the function at each of the line circuits is changed due to changes in subscriptions at each terminal device. Moreover, even if the plurality of line circuits are provided within one packaged line circuit card and the function is to be changed only for a part of the line circuits, the line circuit card must be taken out from the system thereby inconveniently suspending the service temporarily at the terminal device served by the system.